Screw tool

ABSTRACT

A screw tool has a direction-reversible catch including clamping members disposed within wedge-shaped clamping spaces between an outer drive ring part (5) and an inner driven core part (8) of approximately triangular shape in cross section, the clamping members are displaceable by a rotatable switch member which is lockable in its switch positions into release with respect to the wedge walls of the corresponding clamping space by drivers acting on the clamping members and blocking the passage of the clamping members into, in each case one of their two clamping positions, and it proposes, in provide for a structurally simple friction-minimized construction wherein each clamping member lies loosely in a clamping space and is displaceable into its clamping position by the rotation of the drive ring part.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a screw tool.

A screw tool is known from Federal Republic of Germany OS 3 344 361, inwhich the driven core part of triangular cross section forms with theouter drive ring part the wedge-shaped clamping spaces for the receptionof roller-shaped clamping members arranged in pairs. Between each pairof clamping members there extends a compression spring which acts onthem and presses the clamping members into the wedge-shaped clampingspaces. The shifting of the clamping members in order to obtaindifferent directions of drive is effected by means of the centrallymounted switch member from which drivers bent off at an angle extend. Inthis connection, three such drivers are provided, they extending in eachcase between a pair of the clamping members. For the free rotatabilityof the drivers the triangle corners are cut off concentricaly to thecenter of rotation so that the drivers can move there into the adjacentclamping spaces, regardless of the direction in which the driving of thedriven core part is desired. For the fixing of the switch member in itsswitch positions there is provided a detent ball which is arranged inthe driven core part and which cooperates with the switch member. Asidefrom the structural shape which is expensive from a standpoint ofmanufacture, as a result of the large number of structural parts,unfavorable frictional conditions exist which upon longer use of thescrew tool, lead to premature phenomena of fatigue.

SUMMARY OF THE INVENTION

The object of the present invention is to simplify the construction of ascrew tool of the type in question and develop it in such a manner thatfriction is minimized so as to obtain optimum operating conditions. Thisobject is achieved by one clamping member each (24, 58) lies loosely init clamping space and is displaceable into its clamping position by therotation of the drive ring part (3, 34).

As a result of this development, a screw tool of this type which is ofincreased value of use is obtained. The construction of the screw toolis simplified because of the reduced number of parts. It has been foundthat three clamping members are sufficient in order to obtain thedesired action. If the switch member and thus the drive means are in aneutral central position then the driven core part is carried along uponthe rotation of the drive ring part in each direction, the clampingmembers being carried along into their clamping position exclusively bythe rotation of the drive ring part. If, on the other hand, driving inone direction and free travel in the other direction are desired, thenthe switch member must be turned into the corresponding position, inwhich case the drivers block the access to one clamping corner of theclamping space. Upon drive along in rotation the clamping members nowengage into the corresponding clamping corners. A turning of the drivering part in the direction of free travel then leads to the rolling ofthe clamping members out of said clamping corners. It has been foundthat this loose insertion of the clamping members results in a reductionin friction of about 20% as compared with traditional structural shapesso that premature phenomena of fatigue upon lengthy operation of thescrew tool are counteracted. This is of particular importance when thescrew tool is developed as a screwdriver. Barreling of the sides of thetriangular driven core part leads to a continuous guiding of theclamping members into the corresponding clamping corners of the clampingspaces. In this way protection against overload is obtained which leadsto a lengthening of the life of the screw tool. In order to develop thebarreled triangle sides free from incisions, the driven core part bearsthe spring-loaded detent ball in a blind hole along one of its anglebisectors. The corresponding detent depressions which cooperate with theball are located on the inner wall of the cup-shaped switch member. Inthis way defined switch positions can be favorably obtained so that thedrivers of the switch member which are developed as axially protrudingfingers enter in accordance with their purpose into the correspondingposition. A stable supporting feature of the switch member is the drivencore part which has concentrically extending guide surfaces which aretransverse to the angle bisectors and rest against the cup inner wall ofthe switch member. The bearing length of the switch member is furtherincreased by the central guide collar of the driven core part whichenters into the bore in the bottom of the cup of the switch member. Theguide sleeve provides a low-friction and nevertheless stable support forthe driven core part. The guide sleeve which is equipped with bearingribs and is arranged turnably in the inner body of the screwdriverhandle. This inner body is a part of the drive ring part, which leads toa further saving of structural parts. Furthermore, the ribs are providedon the end regions of the guide sleeve so that even large canting forcesare dependably counteracted. A stable interpolation is assured theroller-shaped clamping members so that a part of their end surface restsagainst bottom surfaces whichare formed in the region of the clampingspaces by protrusions of the driven core part. It is possible to producethe barrelled sides of the triangle in the case of polygonal turning bymeans of single-tooth fly cutter. This also results in the outer edgesof the bottom surfaces and of the guide surfaces supplementing eachother to form a circle, together with advantages from a manufacturingstandpoint. Optimum control of the clamping members is obtained by thedrivers of the switch member which extend to the bottom surfaces. Inthis way the axial length of the clamping members corresponds to that ofthe drivers. The surface of the cup edge of the switch member securesthe position of the clamping members in the other direction by grippingthe other end surfaces of the roller-shaped clamping members. The detentdepressions thereof are so developed that the middle one corresponds ina form-locked manner to the ball entrance cross section. The twoadjacennt detent depressions are, however, enlarged in the direction ofrotation and provided with a concave bottom. Depending on the directionof rotation of the switch member, the detent ball then dips into thecorresponding adjacent detent depression and is brought into thecentering position by the compression spring which acts upon it. In thisway, the switch member can move over a larger path and this embodimentalso makes it possible, upon displacement of the drive ring part in thedirection of free-travel, for a slight evasion movement of the driversto also be obtained without the switch member moving out of its switchposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in enlarged size a longitudinal section through the screwtool according to the first embodiment associated with a screwdriverhandle, the switch member being in the center position.

FIG. 2 is a section along the line II--II of FIG. 1.

FIG. 3 is a section along the line III--III of FIG. 1.

FIG. 4 is a section corresponding to FIG. 2, the switch member beingshifted into a different switch position in order to change thedirection of drive.

FIG. 5 is a section similar to FIG. 3, but with the switch ring shifted.

FIG. 6 shows on a larger scale a longitudinal section through the screwtool in accordance with the second embodiment.

FIG. 7 is a section along the line VII--VII of FIG. 6.

FIG. 8 is a view corresponding to FIG. 7 but with the switch memberturned into the one switch position.

FIG. 9 is also a cross section corresponding to FIG. 7, with the switchmember moved into the other switch position.

FIG. 10 is a section along the line X--X of FIG. 6, and

FIG. 11 is a section along the line XI--XI of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The screw tool developed as a screwdriver in accordance with the firstembodiment shown in FIGS. 1 to 5 has a screwdriver handle 1 which isprovided with an axially arranged inner member 2. The latter is seated,non-rotatably, in the screwdriver handle 1 and at its lower end forms adrive ring part 3 of larger cross section; see FIG. 1. In the free endof the drive ring part 3 there are produced stepped bore sections 4, 5,6 in such a manner that the bore sections 4, 5 lie along the height ofthe drive ring part 3. The bore section 6 of smaller cross section whichextends within the inner member 2 receives for rotation a bearing sleeve7 which is equipped with rotating baring ribs 7',7", said sleeve beingintegral with a driven core part 8 arranged within the drive ring part3. The driven core part 8 which is of triangular cross section hasbarrel-shaped triangle sides 9. Their degree of curvature is less thanthat of the wall of the bore section 5. The driven core part 8 formsguide surfaces 9' which are concentric to the bore section 5 andtransverse to the angle bisectors, said guide surfaces connecting thetriangle sides 9 to each other. The barreled triangle sides 9 are formedby polygonal turning, as a result of which protrusions 10 which rest onthe bottom of the bore section 5 are formed. Their outer edges 10' andthe guide surfaces 9' supplement each other to form a circle; see inparticular FIGS. 2 and 4.

On the other side of the free end of the drive ring part 3, the drivencore part 8 continues in a stepwise guide collar 11. Adjoining thelatter there is a stepwise stepped-down extension 11'. The latter servesto receive a clamping spring 12 indicated in dash-dot line, for thefrictional holding of a screwdriver insert part of hexagonal crosssection. For the reception thereof a hexagonal opening 13 is provided inthe driven core part 8 on the other side of the clamping spring 12, abore 13' of larger cross section which passes through the bearing sleeve7 adjoining it.

The guide collar 11 of the driven core part 8 passes through a bore 14in the cup bottom 15' of a cup-shaped switch member 15. The cup rimsurface 15" thereof extends in front of the transition step between thebore sections 4 and 5 and forms there an outwardly directed collar 15'".A lock spring washer 16 which engages into an inner groove 4' of thebore section 4 places itself in front of said collar and holds theswitch member 15 and thus also the driven core part 8 in its axiallynon-displaceable position with respect to the drive ring part 3.

The guide surfaces 9' plus driven core part 8 lie against the cup innerwall 15"" and thus increase the bearing length of the switch member 15.Three drivers 17 located at equal angular distance apart extend from thecup rim surface 15". They are shaped as axially protruding fingers andare integral with the switch member 15. The switch member 15 includingthe drivers 17 can be made of plastic. At the height of one driver 17the switch member 15 is equipped with groove-shaped detent depressions18, 19 and 19' which extend in axial direction and cooperate with adetent ball 20 of the driven core part 9. For this purpose, the drivencore part 8 is provided on one of its angle bisectors with a blind core21 to receive the detent ball 20 and a compression spring 12 which urgesthe ball in outward direction. In accordance with FIGS. 1 to 3, theprotruding region of the detent ball 20 engages in form-locked mannerinto the central detent depression 18 so that in this position alldrivers 17 are opposite the guide surfaces 9' of the driven core part 8of triangular cross section. The two detent depressions 19, 19' whichare directly adjacent the central detent depression 18 are enlarged indirection of rotation and provided with a concave bottom.

The inner surfaces 17' of the drivers 17 are aligned with the cup innerwall 15"" while the outer surfaces 17" are guided by the wall of thebore section 5 of the drive ring part 3. Otherwise, the drivers 17extend up to the protrusions 10 of the driven core part 8; see FIG. 1.

Between the triangle sides 9 of the driven core part 8 and the wall ofthe bore section 5 clamping spaces 23 are formed. Each of these clampingspaces 23 forms clamping cornners 23' in its circumferential endregions. In each clamping space 23 there loosely lies a roller-shapedclamping member 24. In the central switch position of the switch member15 the clamping members 24 lie approximately on a line with the vertexof the barreled triangle sides 9; see FIGS. 2 and 3.

The roller-shaped clamping members 24 have a part of their one endsurface 25 in front of the bottom surfaces 10" of the protrusions 10 andare accordingly secured in position in one direction by them. Thesecuring in position in the other direction is imparted to the clampingmembers 24 by the cup rim surface 15" of the switch member 15 whichengages over the other end surface 26. Since the drivers 17 extend tothe bottom surfaces 10" of the protrusions 10 or even slightly beyondthem, along radial control surfaces 17'" are present on the drivers 17.

This embodiment operates as follows:

If the switch member 15 is in the central switch position (see FIGS. 1to 3), then, upon the turning of the screwdriver handle 1, the drivencore part 8 is carried along in each direction by means of the drivering part 3, due to the entraining of the clamping members 24 into thecorresponding clamping corners 23'. Free travel then does not takeplace.

If, on the other hand, the driven core part 8 is to be carried along inthe direction of the arrow y in accordance with FIGS. 4 and 5, then theswitch member 15 must be turned in such a way that the detent ball 20engagably enters the detent depression 19. The drivers 17 extending fromthe switch member 15 thereby displace the clamping members 24 by acertain amount from their center position in the direction towards thecorresponding clamping corner 23' of the clamping spaces 23. If thedrive ring part 3 or the screwdriver handle 1 is now turned in thedirection indicated by the arrow y, then, due to friction, thisdisplaces the clamping members into the clamping position so that inthis way the driven core part 8 is also rotates in the directionindicated by the arrow y. Upon the opposite direction of rotation, theclamping members 24 are displaced from the corresponding corners 23',which corresponds to free travel. The drivers 17 and thus the switchmember 15 can possibly be turned slightly by the clamping members 24.Nevertheless, the detent ball 20 remains in its detent depression 19.

If the driven core part 8 is to be driven in the other direction ofrotation, then the switch member 15 must be turned in such a way thatthe detent ball 20 enters into the detent depression 19'.

In accordance with the second embodiment, shown in FIGS. 6 to 11, thescrew tool has a screwdriver handle 32 to receive the sleeve 33 of adrive ring part 34. Within the sleeve 33 there is rotatably arranged abearing bushing 35 of a driven core part 36. In order to obtain reducedfriction between the sleeve 33 and the bearing bushing 35, the bearingbushing 35 forms an annular groove 37 into which bearing balls 38 of thesleeve 33 engage. The bearing balls 38 are seated in three radial bores29 of sleeve 33 which are arranged at equal circumferential distancesapart; see in particular FIG. 10. At the place of the radial bores thereis a spring washer 40 which is introduced from the outside into thesleeve 33. It prevents plastic material from coming into the radialbores 39 upon the spraying-on of the handle 32 which is to be made fromplastic.

A bore 41 is produced starting from the end surface 34' of the drivering part 34. Within it the driven core part 36 which forms anequilateral driven triangle is rotatably mounted in such a manner thatthe vertices 36' of the triangle are guided on the inner wall 41' of thebore 41.

The bearing bushing 35 of the driven core part 36 rotatably receives astepped tubular shank 42 of a tool-holder sleeve 43. The sleeve ishexagonal in cross section and the end of it which faces the shank 42enters in form-locked manner into a triangular recess 44 in the drivencore part 36. The inner surfaces 44' of the triangular recess 44 extendin this connection parallel to the triangle sides 36" of the triangulardrive core part 36. In this way, wall sections 45 which are directedalong a triangle are created which come into form-lock with thecorresponding polygonal surfaces of the tool-holder sleeve 43. The outerend surfaces 45' of these wall sections 45 which form triangle sides arebeveled. The recess 44 is opened in the region of the vertices 36' ofthe triangle by slitting 46. In this way, detent depressions 47 areformed in the region of the triangle vertices 36' to receive detentballs 48 which form the drivers. The detent balls extend in bores 49 ofa switch member 50 which is rotatably associated with the drive ringpart 34. Three detent balls 48 are provided corresponding to thetriangular driven core part and accordingly also three bores 49 spacedcircumferentially equally apart. The detent balls 48 are acted on bycompression spring 51 which press the detent balls 48 into the detentdepressions 47. For turnable association, the switch member 50 forms onits end surfaces facing the drive ring part 34 an edge-side collar 52which extends into an edge-side annular groove 53 of the drive ring part34. For the passage of the tool-holder sleeve 43, the switch member 50forms a central bore 54. The latter is so large that turnability of theswitch member 50 is assured. The switch member 50 is imparted assuranceagainst being pulled off by a lock washer 55 of the tool-holder sleeve43 on which lock washer 55 the switch member 50 rests.

The tool-holder sleeve 43 on its part is also secured against beingpulled off by a lock washer 56. The latter is seated on the end of theshank 2 of the tool-holder sleeve which extends beyond the bearingbushing 35 and rests against the end surface there of the bearingbushing 35.

The tool-holder sleeve 43 is provided on its inside with a polygonaledge 57 for the insertion of the tool, in order to be able to drive thelatter.

As coupling means between driven core part 36 and drive ring part 34there are employed clamping members 53. The latter are located in theregion between the inner wall 41' of the bore 41 of the drive ring part34 and the wall sections 45 of the driven core part 36. In this waythree segment-like clamping spaces are created. The roller-shapedclamping members 58 are located in the region of the largest radialdimension of these spaces. The clamping members extend to the bottom ofthe bore 41 and terminate flush with the end surface 34' of the drivering part 34 and thus also with the end surface of the driven core part.The ends there of the clamping members are provided with frustoconicalbevels 58'. Each clamping member 58 forms a space divider so thatclamping corner 59, 60 which extend in wedge shape on both sides thereofare produced.

The manner of operation of the screw tool last described is as follows:

If the switch member 50 assumes its central position in accordance withFIGS. 6 and 7, then the detent balls 48 lie in the detent depressions 47within the region of the vertices 36' of the triangle. Upon the turningof the handle 32 or of the drive ring part 34 which is connected, fixedfor rotation, with it, the driven core part 36 is carried along in bothdirections of rotation.

If it is desired that the driven core part 36 be carried along in thedirection of the arrow x in FIG. 8, then the switch member 50 must alsobe turned in that direction. In this case the detent balls 48 arecarried along. They pass through the one slit and pass into the corners59. There they receive a threefold support, in that they come againstthe inner wall 41', against the outer surface of the clamping members58, and against the beveled end surfaces 45' of the wall section 45. Inthis way the clamping members 48 are urged in the direction of theclamping corners 60 so that upon rotation of the drive ring part 34 inthe direction indicated by the arrow x the driven core part 36 is drivenalong. An oppositely directed rotary movement of the drive ring part, onthe other hand, does not lead to any driving along of the drive corepart 36 so that this is the free travel.

FIG. 11, in particular, shows that in the switch position the detentball 48 cannot rest on the bottom of the bore 41 of the drive ring part34. This is important in order to permit the bringing back of the switchmember ring into the central position, in which connection the detentballs after passing through the corresponding slit pass into the detentdepressions 47.

In accordance with FIG. 9, the switch member ring 50 has been turned inthe direction of the arrow y. In this way the detent balls 48 also haveleft the detent depressions 47 and have entered into the clampingcorners 60. There they also receive a three-point support and push theclamping members into the clamping corners 59. Upon a turning of thedrive ring part 34 in the direction of the arrow y, the driven core part36 is therefore also carried along in the direction of this arrow. Theopposite rotation of the drive core part then corresponds to thedirection of free travel.

I claim:
 1. In a screw tool with direction-reversible catch, the toolcomprising an outer drive ring part, and an inner driven core part ofapproximately triangular cross section;a rotatable switch member havinga plurality of drivers extending therefrom and arrangedcircumferentially around said core part; clamping members inwedge-shaped clamping spaces between said outer drive ring part and saidinner driven core part, which clamping members are displaceable by saidrotatable switch member which is lockable in its switch positions, eachof said wedge-shaped clamping spaces having two clamping positions atopposite ends of a clamping space for receiving and clamping one of theclamping members; and wherein said drivers act on the clamping membersand block passage of the clamping members into respectively one of theirtwo clamping positions and wherein; in two switch positions of theswitch member, each of said clamping members is loosely disposed in aseparate of said clamping spaces and is displaceable into a clampingposition therein exclusively by rotation of the drive ring part; in acentral switch position of said switch member, each of said clampingbodies is located substantially centrally to a corresponding side ofsaid driven core part; vertices of said core part are arrangedconcentrically about said core part to separate said clamping spaces,said drivers being located at respective ones of said vertices and beingtranslatable in circumferential direction relative to said vertices uponrotation of said switch member about said core part; and said driversextend in circumferential direction into said clamping spaces to limitmovement of said clamping members in said clamping spaces to apredetermined region of unobstructed movement, a circumferentiakl lengthof said predetermined region of unobstructed movement beingapproximately equal to a circumferential length of a driver.
 2. A screwtool according to claim 1, whereinsaid driven core part has said sidesformed with barreled shape with a smaller degree of curvature than thatof said drive ring part.
 3. A screw tool according to claim 1,whereinsaid driven core part carries a spring-loaded detent ball on oneof its angle bisectors in a blind bore, detent depressions opposite saidball, said detent depressions being formed on an inner wall of saidswitch member, the latter having said drivers in the form of axiallyprotruding fingers, said switch member being cup-shaped.
 4. A screw toolaccording to claim 3, whereinsaid driven core part forms concentricallyextending guide surfaces disposed transverse to said angle bisectors andwhich rest against said cup inner wall.
 5. A screw tool according toclaim 3, whereinsaid driven core part has a central guide collar adaptedto enter into a bore within a cup bottom of said switch member.
 6. Ascrew tool according to claim 5, whereinsaid driven core part has,opposite the guide collar, a guide sleeve which protrudes into ascrewdriver handle inner member, said sleeve having a wall surfaceprovided with bearing ribs bearing against said inner member, and saidinner member is one-piece with said drive ring part.
 7. A screw toolaccording to claim 1, whereinsaid clamping members are shaped as rollersand rest only with a part of one of their end surfaces on bottomsurfaces formed in the region of said clamping spaces by protrusions ofsaid driven core part.
 8. A screw tool according to claim 7,whereinouter edges of the bottom surfaces and guide surfaces of saiddriven core part supplement each other to form a circle.
 9. A screw toolaccording to claim 7, whereinsaid drivers extend to the bottom surfacesand said clamping members have axial lengths corresponding to that ofthe drivers so that another end surface of the clamping members isgripped by a cup rim surface of said switch member, said switch memberbeing cup-shaped.
 10. A screw tool according to claim 3, whereinsaiddetent depressions provided three switch positions and comprise acentral one of said detent depressions corresponding to said centralswitch position which is operative in both directions of rotation andhas a shape complementary to said detent ball, and two of said detentdepressions directly adjacent said central detent depression which areeach enlarged in shape in the directions of rotation and each providedwith a concave bottom.
 11. A screw tool according to claim 1,whereinsaid switch member in said switch positions is lockable indifferent relative positions to said driven core part.
 12. A screw toolaccording to claim 11, whereinsaid drive ring part and said driven corepart are relatively rotatably mounted.
 13. A screw tool according toclaim 1, whereinin said central switch position said drivers areadjacent lateral ends of said sides of said driven core part and spacedapart from said clamping members.
 14. A screw tool according to claim 1,whereinin said two switch positions of said switch member said driversare adjacent said clamping members.
 15. A screw tool according to claim8, whereinsaid guide surfaces of said driven core part relativelyrotatably engage on an inner wall of said switch member. .Iadd.
 16. In ascrew tool with direction-reversible catch, the tool comprising an outerring part, and an inner core part of approximately polygonal crosssection;a rotatable switch member having a plurality of driversextending therefrom and arranged circumferentially around said corepart, said switch member being lockable in a plurality of switchpositions; plural clamping members disposed around said core part, saidclamping members being located in wedge-shaped clamping spaces betweensaid outer ring part and said inner core part, said clamping membersbeing displaceable by said rotatable switch member, each of saidwedge-shaped clamping spaces having two clamping positions at oppositeends of a clamping space for receiving and clamping one of the clampingmembers; and wherein said drivers act on the clamping members to limitpassage of each clamping member within one of its two clampingpositions; in two switch positions of the switch member, each of saidclamping members is loosely disposed in a separate one of said clampingspaces and is displaceable into a clamping position therein by rotationof the ring part; in a central switch position of said switch member,each of said clamping bodies is located substantially centrally of acorresponding side of said core part; vertices of said core part arearranged concentrically about said core part to define said clampingspaces, said drivers being located at respective ones of said verticesand being translatable in circumferential direction relative to saidvertices upon rotation of said switch member about said core part; andsaid drivers limit movement in circumferential direction within each ofsaid clamping spaces of said clamping members to a predetermined regionof unobstructed movement, a circumferential length of said predeterminedregion of unobstructed movement being greater than approximately twicethe diameter of a clamping member. .Iaddend. .Iadd.17. In a screw toolwith direction-reversible catch, the tool comprising an outer ring part,and an inner core part of approximately polygonal cross section; arotatable switch member having a plurality of drivers extendingtherefrom and arranged circumferentially around said core part, saidswitch member being lockable in a plurality of switch positions; pluralclamping members disposed around said core part, said clamping membersbeing located in wedge-shaped clamping spaces between said outer ringpart and said inner core part, said clamping members being displaceableby said rotatable switch member, each of said wedge-shaped clampingspaces having two clamping positions at opposite ends of a clampingspace for receiving and clamping one of the clamping members; andwherein said drivers act on the clamping members to limit passage ofeach clamping member within one of its two clamping positions; in twoswitch positions of the switch member, each of said clamping members isloosely disposed in a separate one of said clamping spaces and isdisplaceable into a clamping position therein by rotation of the ringpart; in a central switch position of said switch member, each of saidclamping bodies is located substantially centrally of a correspondingside of said core part; vertices of said core part are arrangedconcentrically about said core part to define said clamping spaces, saiddrivers being located at respective ones of said vertices and beingtranslatable in circumferential direction relative to said vertices uponrotation of said switch member about said core part; said core partcarries a spring-loaded detent ball, and three detent depressions areformed on a wall of said switch member for providing three of saidswitch positions; and said detent depressions include a central detentdepression corresponding to said central switch position which isoperative in both directions of rotation of said switch member and has ashape complementary to said detent ball, said detent depressions furthercomprising two further detent depressions disposed on opposite sides ofsaid central detent depression, the two further detent depressions beingenlarged relative to the central depression in the directions ofrotation of said switch member. .Iaddend. .Iadd.18. A screw toolaccording to claim 17, whereinsaid polygonal cross section is atriangular cross section. .Iaddend. .Iadd.19. A screw tool according toclaim 17, wherein each of said further detent depressions is formed witha curved concave surface. .Iaddend. .Iadd.20. A screw tool according toclaim 19, whereina radius of curvature of the concave surface of each ofsaid further detent depressions is larger than a radius of curvature ofsaid detent ball. .Iaddend. .Iadd.21. A screw tool according to claim17, wherein a cross-sectional dimension of each of said further detentdepressions is larger than a cross-sectional dimension of said detentball. .Iaddend. .Iadd.22. A screw tool according to claim 17, wherein anenlargement of each of said further detent depressions relative to saidcentral depression is sufficient to allow for movement of the detentball in either of said further detent depressions in a direction ofrotation of said switch member. .Iaddend. .Iadd.23. In a screw tool withdirection-reversible catch, the tool comprising an outer ring part, andan inner core part of generally polygonal cross section;a rotatableswitch member having a plurality of drivers extending therefrom andarranged circumferentially around said core part, said switch memberbeing lockable in a plurality of switch positions; plural clampingmembers disposed around said core part, said clamping members beinglocated in wedge-shaped clamping spaces between said outer ring part andsaid inner core part, said clamping member being displaceable by saidrotatable switch member, each of said wedge-shaped clamping spaceshaving two clamping positions at opposite ends of a clamping space forreceiving and clamping one of the clamping members; and wherein saiddrivers act on the clamping members to limit passage of each clampingmember within one of its two clamping positions; in two switch positionsof the switch member, each of said clamping members is loosely disposedin a separate one of said clamping spaces and is displaceable into aclamping position therein by rotation of the ring part; in a centralswitch position of said switch member, each of said clamping bodies islocated substantially centrally of a corresponding side of said corepart; vertices of said core part are arranged concentrically about saidcore part to define said clamping spaces, said drivers being located atrespective ones of said vertices and being translatable incircumferential direction relative to said vertices upon rotation ofsaid switch member about said core part; said core part carries aspring-loaded detent element having a curved surface, and three detentdepressions are formed on a wall of said switch member for providingthree of said switch positions; and said detent depressions include acentral detent depression corresponding to said central switch positionwhich is operative in both directions of rotation of said switch memberand has a shape complementary to said detent element, said detentdepressions further comprising two further detent depressions disposedon opposite sides of said central detent depression, the two furtherdetent depressions being enlarged relative to the central depression inthe directions of rotation of said switch member to permit movement ofsaid detent element within either of said further detent depressions..Iaddend. .Iadd.24. A screw tool with direction-reversible catch, thetool comprising an outer ring part, and an inner core part ofapproximately polygonal cross section; a rotatable switch member havinga plurality of drivers extending therefrom and arrangedcircumferentially around said core part, said switch member beinglockable in a plurality of switch positions; plural clamping membersdisposed around said core part, said clamping members being located inwedge-shaped clamping spaces between said outer drive ring part and saidcore part, said clamping members being displaceable by said rotatableswitch member, each of said wedge-shaped clamping spaces having twoclamping positions at opposite ends of a clamping space for receivingand clamping one of the clamping members; and wherein said drivers acton the clamping members to limit passage of each clamping member withinone of its two clamping positions; in two switch positions of the switchmember, each of said clamping members is disposed in a separate one ofsaid clamping spaces and is displaceable into a clamping positiontherein by rotation of said ring part relative to said core part;constrictions of said clamping spaces are arranged concentrically aboutsaid core part, said drivers being located at respective ones of saidconstrictions and being translatable in circumferential directionthrough respective ones of said constrictions upon rotation of saidswitch member about said core part; said screw tool further comprisesdetent means for positioning said switch member relative to theconstrictions of said clamping spaces, said detent means including adetent element movable in radial direction and fixed in circumferentialdirection relative to said constrictions, said detent means including anarrangement of detent depressions disposed on said switch member forreceiving said detent element; and a first and a second of said detentdepressions are disposed on opposite sides of a center of saidarrangement of detent depressions, said first and said second detentdepressions being enlarged relative to said detent element in thedirections of rotation of said switch member to permit movement of saiddetent element within either of said first and said second detentdepressions. .Iaddend. .Iadd.25. A screw tool with direction-reversiblecatch, the tool comprisingan outer ring part, and an inner core part ofgenerally polygonal cross section; a rotatable switch member having aplurality of drivers extending therefrom and arranged circumferentiallyaround said core part, said switch member being lockable in a pluralityof switch positions; plural clamping members disposed around said corepart, said clamping members being located in wedge-shaped clampingspaces between said ring part and said core part, said clamping membersbeing displaceable by said rotatable switch member, each of saidwedge-shaped clamping spaces having two clamping positions at oppositeends of a clamping space for receiving and clamping one of the clampingmembers; and wherein said drivers act on the clamping members to limitpassage of each clamping member within one of its two clampingpositions; in two switch positions of the switch member, each of saidclamping members is disposed in a separate one of said clamping spacesand is displaceable into a clamping position therein by rotation of saidring part relative to said core part; constrictions of said clampingspaces are arranged concentrically about said core part, said driversbeing located at respective ones of said constrictions and beingtranslatable in circumferential direction through respective ones ofsaid constrictions upon rotation of said switch member about said corepart; and said screw tool further comprises a spring-loaded detentelement having a curved surface, and an arrangement of plural detentdepressions are formed on a wall of said switch member for receivingsaid detent element to provide said switch positions; and a first and asecond of said detent depressions are disposed on opposite sides of acenter of said arrangement of detent depressions, said first and saidsecond detent depressions being enlarged relative to said detent elementin the direction of rotation of said switch member to permit movement ofsaid detent element within either of said first and said second detentdepressions. .Iaddend. .Iadd.26. A screw tool with direction-reversiblecatch, the tool comprisingan outer ring part, and an inner core part ofapproximately polygonal cross section; a rotatable switch member havinga plurality of drivers extending therefrom and arrangedcircumferentially around said core part, said switch member beinglockable in a plurality of switch positions; plural clamping membersdisposed around said core part, said clamping members being located inwedge-shaped clamping spaces between said ring part and said core part,each of said wedge-shaped clamping spaced having two clamping positionsat opposite ends of a clamping space for receiving and clamping one ofsaid clamping members; wherein said clamping members are displaceable bysaid switch member into a clamping position of a respective clampingspace and provide a clamping upon rotation of said ring part relative tosaid core part; said drivers are operable to limit passage of eachclamping member within its clamping space to one of its two clampingpositions; constrictions of said clamping spaces are arrangedconcentrically about said core part, said drivers being located atrespective ones of said constrictions and being translatable incircumferential direction through respective ones of said constrictionsupon rotation of said switch member about said core part; and saiddrivers limit movement in circumferential direction within each of saidclamping spaces of said clamping members to a predetermined region ofunobstructed movement, a circumferential length of said predeterminedregion of unobstructed movement being greater than approximately twicethe diameter of a clamping member. .Iaddend.